Gate valves may be used to control the flow of fluid in conduits. Some applications where gate valves are used are characterized by high temperatures (e.g. in excess of 350° C.) and/or pressures (e.g. in excess of 15,000 kPa). The pressure and temperature ratings of gate valves are typically characterized by the American Society of Mechanical Engineers (ASME) or other similar nationally or internationally recognized institutions. Specifically, the standard ASME B16.34 covers valves—flanged, threaded and welded end—and specified allowable maximum pressures and temperatures. Relatively recently, gate valves have been constructed with relatively large cross-sectional sizes (e.g. in excess of 20 inches in diameter) and to pressure and temperature ratings according to ASME B16.34 Class 600 and higher. Non-limiting examples of applications where such gate valves are used include steam assisted gravity drain (SAGD) oil extraction, hydrocarbon or other chemical processing, steam turbine power generation, steam generation and/or processing applications, other steam-based applications and/or the like.
FIG. 1 shows a partial cross-section view of a prior art gate valve 100 of the type currently used for applications characterized by high temperatures and pressures (e.g. ASME B16.34 Class 600 or higher). Valve 100 comprises a valve body 110 which defines a flow passageway 112 between an inlet port 114 and an outlet port 116. Valve 100 is typically installed along a conduit, connected at inlet port 114 to an upstream conduit and at outlet port 116 to a downstream conduit.
A first seat ring 120 is installed at inlet port 114. A second seat ring 130 is installed at outlet port 116. Seat rings 120, 130 respectively comprise seat faces 122, 132. Where high temperatures and/or pressures preclude or otherwise make it inconvenient to use elastomer gaskets, seat rings 120, 130 are respectively secured in ports 114, 116 using annular welds 124, 134. A stem 150 is movable to drive obturator 160 against seat rings 120, 130. In the illustrated gate valve 100, stem 150 may be lowered to respectively press the outward faces 164, 166 of obturator 160 against faces 122, 132 of seat rings 120, 130 (i.e. closing valve 100) and stem 150 may be raised to move outward faces 164, 166 of obturator 160 away from faces 122, 132 of seat rings 120, 130 (i.e. opening valve 100). Because of the shape of obturator 160, valve 100 may be referred to as a wedge-gate valve.
In use of valve 100, seat faces 122, 132 may become worn or the quality of seat faces 122, 132 may otherwise deteriorate. By way of non-limiting example, such wear and/or quality deterioration may occur due to friction with obturator 160, debris in fluid passing through valve 100, corrosion, and/or the like. Worn or otherwise degraded seat faces 122, 132 are associated with poor sealing between obturator 160 and seat rings 120, 130. Such poor seals can cause valve 100 to leak, to function inefficiently and/or to cease functioning at an acceptable level or altogether. Such poor seals can cause also cause further damage to valve 100 (e.g. further degradation of seat faces 122, 132 or the like) and/or to other parts of the system (not shown) in which valve 100 is operating.
Servicing prior art valve 100 (e.g. because of worn or otherwise degraded seat faces 122, 132) typically involves removing valve 100 from the conduit and either replacing valve 100 or transporting valve 100 to a suitable location (e.g. a machine shop) for servicing. Once valve 100 is removed from the conduit and transported to a service location, servicing valve 100 may involve cutting welds 124, 134 to facilitate the removal of seat rings 120, 130, removing seat rings 120, 130 from valve 100 and either replacing seat rings 120, 130 with new seat rings or resurfacing seat faces 122, 132 using suitable machining techniques (e.g. grinding). Because of this process, servicing prior art valve 100 (e.g. because of worn or otherwise degraded seat faces 122, 132) can be time consuming, costly and dangerous. Moreover, the system in which valve 100 operates has to be shut down while valve 100 is being services which can exacerbate the costs associated with servicing valve 100.
U.S. Pat. No. 3,175,802 and U.S. Pat. No. 3,689,028 purport to describe valve assemblies having removable seat rings. These valve assemblies are not suitable for services in valves having large cross-sectional area (e.g. greater than 20 inches in diameter) and/or in pressure and temperatures designated by ASME B16.34 as class 600 or higher.
There is a general desire for valves and/or seat rings wherein the seat rings are easily removed from the valves and new or refurbished seat rings are easily replaced into the valves in situ (e.g. without disconnecting the valve bodies from their associated upstream or downstream conduits) and corresponding methods for in situ removal of seat rings from, and replacement of seat rings into, valves. There is a further desire for such valves, seat rings and methods to have application in high temperature and/or high pressure environments.